The subject matter disclosed herein relates to patch repair and, more specifically, environmentally resistant patches for filling voids in silicon-containing components, such as silicon carbide (SiC) based ceramic matrix composites (CMCs).
Environmental barrier coatings (EBCs) protect gas turbine components fabricated from silicon-containing substrates from exposure to potentially harmful chemical environments in service. Examples of silicon-containing substrates include SiC based CMCs, SiC or silicon nitride (Si3N4) based monolithic ceramics, and metal silicides, such as Mo—Si—B and Nb—Si based composites. Examples of EBCs include alkaline earth aluminosilicates (e.g., barium-strontium aluminosilicate, or BSAS), rare earth (RE) monosilicates having the general composition RE2SiO5 and RE disilicates having the general composition RE2Si2O7. The RE elements can include La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and/or Lu, and the rare earth-like elements Y and/or Sc. EBCs are generally selected to have a good match in their coefficient of thermal expansion (CTE) to that of the silicon-containing substrate material.
Some EBC materials are deposited on components using a plasma spraying process. The plasma spraying process provides flexibility to deposit a large variety of materials within a wide coating thickness range (ranging from about 0.001 inch to about 0.080 inch) without major process modifications.
Furthermore, if an EBC experiences a localized spall or a pinhole defect, the underlying CMC may be subject to cavitation resulting from water vapor induced volatilization and subsequent surface recession during service. If allowed to grow unmitigated, such cavities may reduce the load-bearing capability of the component, disrupt airflow, or even progress to through-thickness holes that lead to ingestion of combustion gases or leakage of high-pressure cooling air, thus adversely affecting operating efficiency and durability of the machine. Furthermore, depending on the type and application of the turbine component, surfaces may similarly require modification via turbine component patch materials for a variety of other reasons.
Accordingly, materials and methods for modifying surfaces such as by filling surface-connected voids in turbine components would be welcome in the art.